Thunderbird Android doesn't send emails with custom domain+provider

Checklist

• I have used the search function to see if someone else has already submitted the same bug report.
• I will describe the problem with as much detail as possible.

App

Thunderbird for Android

App version

8.2

Where did you get the app from?

None

Android version

15 AQ3A.240912.001 (HyperOs 2.0.4.0)

Device model

Redmi Note 13 Pro 5G

Steps to reproduce

Hi all,

I have installed Thunderbird Android and correctly set an IMPA account.
It is not a "provider" email (eg, Gmail, yahoo, etc), it is my own email using my domain+provider.

I am able to receive emails, no problem there.
But I am not able to send any email.

After I tap "send", emails are moved to the "sent" folder, but they are never delivered (they don't go to spam).
I have also checked the settings with my provider, that hosts my email, all is correct.

Additional context.

• If I send an email to myself (same from/to email address), that is sent.
• I have tried K-9 with the same settings, it doesn't work neither.
• I have tried FairEmail and BlueMail apps with the exact same settings, and YES emails are correctly delivered using those apps.

Thanks

Expected behavior

Emails should be sent using my custom email+hosting

Actual behavior

Emails are moved to "sent" folder but they are actually not sent.

Other apps like fairemail and BlueMail work well and send the emails (using the exact same setting)

Logs

No response

The report names no source file, test, or log. Start by reproducing the failed send on Thunderbird for Android 8.2 with the reported custom-domain provider, then compare the send behavior and available diagnostics with FairEmail or BlueMail. Done means messages are delivered to external recipients, not merely moved to Sent.